High blood pressure is a strong risk factor for cardiovascular, cerebrovascular, and kidney disease. Although highly heritable, the genetic basis of blood pressure variation in the general population has been poorly-defined. In preliminary work, a common genetic variant associated with blood pressure was identified at the GUCY1A3/GUCY1B3 locus, which encodes the alpha1 and beta1 subunit of soluble guanylate cyclase, an enzyme which synthesizes cGMP when activated by nitric oxide and which is abundantly expressed in the vasculature. Among up to 200,000 individuals of European ancestry, 58% of the population has two copies of a BP-raising allele. The overall goal of the proposed research program is to ascertain whether the GUCY1A3/GUCY1B3 genetic variant associated with blood pressure (or a closely linked variant) modulates expression of soluble guanylate cyclase alpha1 and/or beta1 subunits. In Aim 1, we seek to establish whether the association of BP with the SNP at the GUCY1A3/GUCY1B3 locus is likely to be determined by a difference in sGC activity. Inhaled nitric oxide will be administered to individuals with 0 or 2 copies of the BP-raising allele, and the impact of genotype on the ability of NO inhalation to increase plasma cGMP levels will be determined. In parallel experiments, platelet soluble guanylate cyclase subunit mRNA and protein levels, as well as enzyme activity and NO- inhabitable aggregation will be compared between genotypes. In Aim 2, genetic variants will be introduced into bacterial artificial chromosomes containing the human GUCY1A3/GUCY1B3 locus. Clones containing major and minor alleles will be introduced in vascular smooth muscle cells, and expression of the soluble guanylate cyclase alpha1 and beta1 subunits will be compared. The investigators' proposed use of detailed physiologic phenotyping and molecular characterization of the DNA sequence variation promises to yield fundamental insights into regulation of the GUCY1A3 and GUCY1B3 genes and to begin to better understand the role of nitric oxide-soluble guanylate cyclase-cGMP signaling in blood pressure regulation in the general population.